Exploring a novel nitrogen biogeochemical cycle and its dynamics in a contaminated aquifer

Cornell University, Ithaca NY

Investigators

Abstract

This project seeks to advance understanding of the roles that microorganisms play in detoxifying ground waters polluted with organic compounds. The complex microbial communities that dwell in subsurface habitats have the capability of metabolizing organic contaminants. When this occurs, the metabolic processes (e.g., biodegradation) carried our by one set of microbial populations can lead to the accumulation of byproducts that may foster growth and metabolism of another set of populations. This project aims to reveal the intricate interactions (processes and controls) between microbial populations that reside in a shallow aquifer in South Glens Falls, NY that is contaminated with aromatic hydrocarbon-rich coal tar waste. Naphthalene is a key pollutant there. Understanding how the microbially-mediated processes alter site geochemistry and how site geochemistry (in turn) alters microbial reactions and is a central goal. The fundamental hypothesis of this project is that a novel nitrogen cycle has developed on site due to three interacting factors: (i) the influx of naturally occurring nitrate in groundwater; (ii) anaerobic microbial metabolism of the aromatic hydrocarbons leading to an accumulation of ammonia and methane, and (iii) fluctuating oxidation-reduction (redox) conditions that control physiological reactions carried out by the microorganisms. Seven auxiliary hypotheses to be tested within this project examine the detailed interactions of microbial populations and the specific genes they express to catalyze these reactions that both destroy pollutants and influence water quality. To test these hypotheses, we will: routinely monitor the geochemical status of the site; routinely assess the composition of microbial communities across the site using molecular fingerprinting techniques; implement a series of laboratory-based determinations of nitrogen-cycle processes (especially dissimilatory reduction of nitrate to ammonia, DNRA), complete a complementary array of molecular biological field assays characterizing the naturally occurring communities and their expressed functional genes; and integrate the entire data set using correlational analyses. This project addresses fundamental questions about the function of naturally occurring microbial communities, the identities of populations active in transforming nitrogen and carbon compounds, and how environmental pollution alters the structure and function of microbial populations that maintain ecosystems. Thus, the information generated advances scholarly areas that span cellular, ecological, and pollution-control issues. Furthermore, this project will contribute to graduate and undergraduate education of project participants and to public educational outreach (via a web site and other activities by the investigator). This project will provide a database on fundamental microbial diversity (of culturable microorganisms, sequences of genes controlling the cycling of both carbon and nitrogen) that will be valuable resources for comparison to the taxonomy and functional roles of microorganisms in other habitats. Rapid, open exchange of geochemical data, microbial cultures, nucleic acid sequences, and biogeochemical processes with other scientists and the public will enhance the impact of this project on society's awareness of the significance of microorganisms in ecosystem function.